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COVID-19

Testing

CORONAVIRUS TESTING BASICS

This 3 minute video in English and Spanish explains the basics of COVID-19 testing

PROTECTING YOURSELF AND OTHERS

  • The best way to reduce the risk of COVID-19 is to practice everyday prevention, including keeping your distance from others, wearing a mask correctly over both your nose and mouth, and washing your hands often. Choose wisely and avoid the 3 C’s (confined spaces, crowding, and close contact).
  • People with COVID-19, even if they have no symptoms, can be very infectious and pass the infection to others.
  • Even if you test negative, it is still important to take steps to protect yourself and others from COVID-19. With widespread community transmission, there is a daily risk of becoming infected with  COVID-19.
  • If you have symptoms, you should stay at home. Talk to a healthcare provider and get tested. For more information, visit ph.lacounty.gov/covidcare.
  • If you have a positive diagnostic (viral) test for COVID-19 or your doctor thinks that you have COVID-19, you must isolate yourself and follow these home isolation instructions closely. If your test was positive, tell all your close contacts that they need to quarantine.
  • If you are a close contact to a person infected with COVID-19, you need to quarantine (stay home; separate yourself from others to “wait and see” if you develop the illness). It is also recommended that you get tested for COVID-19, but you must quarantine the full time even if you get a negative test result. For more information visit http://ph.lacounty.gov/covidquarantine.

TYPES OF COVID-19 TEST

DIAGNOSTIC (VIRAL) TESTS

Shows current infection

ANTIBODY TEST

Shows past infection

Also known as

Molecular Test

  • Diagnostic test
  • Nucleic acid amplification test (NAAT)
  • Reverse-Transcriptase Polymerase Chain Reaction (RT-PCR or PCR)

Antigen Test

  • Rapid diagnostic test

Antibody Test

  • Serology
  • Serological test
  • Blood test

When the test is recommended

  • For people with symptoms of COVID-19
  • For people who were close contacts to COVID-19
  • For people without symptoms living/working in a high risk setting who are identified as part of an outbreak detection and response
  • For people with symptoms of COVID-19 (recommended soon after their symptoms started).
  • Recommended only for certain situations. See “uses of serology
  • NOT for diagnosing a current infection
  • NOT to show a person does not have COVID-19

How the test works

Detects genetic material (RNA) within the COVID-19 virus

Detects proteins (or antigens) on the surface of the COVID-19 virus

Detects antibodies made by the immune system in response to COVID-19 infection

How the test is done
(Type of sample)

Saliva, or swab from nose or throat

Swab from nose or throat

Blood from arm or finger stick

How long it takes to get results

Typically, 2-6 days but some locations offer same day or even one- hour results

Most are rapid, approximately 15 minutes or less.

Same day to 3 days

What the test does

Checks for active coronavirus infection

Checks for active coronavirus infection

Checks for past coronavirus infection

What a positive result means*

A positive result means you have COVID-19. The test detected the COVID-19 virus. 

  • You need to isolate and tell your close contacts to quarantine

NOTE: If you had COVID-19 within the past 90 days and you now have a positive test but no symptoms, talk with your doctor to see if you have COVID-19 again.

A positive result means you have COVID-19. The test detected the COVID-19 virus.

  • You need to isolate and tell your close contacts to quarantine

A positive result means that you have been infected by COVID-19 in the past. The test detected antibodies to the COVID-19 virus.

What a negative result means*

A negative result means the test did not detect the virus at the time the test was taken.

A negative result can also happen if the test was taken too early or the test missed your infection.

Note: If you are a close contact to a person with COVID-19 you must remain under quarantine for the entire time because you may still be infected but it was too early for your test to be positive.

A negative result means the test did not detect the virus at the time the test was taken. 

  • It is recommended that you now get a molecular (PCR) test because antigen tests often miss infections. Stay at home till your PCR test is ready.

Note: If you are a close contact to a person with COVID-19 you must remain under quarantine for the entire time because you may still be infected but it was too early for your test to be positive.

A negative result means the test did not detect antibodies to the COVID-19 virus and you may have never had COVID-19 (see antibody section below).

*No test for COVID-19 is perfect. Any test may produce:

  • False negative results
    • This means that the test result should be positive because you DO have COVID-19, but instead it comes back negative.
    • This may happen, for example, if the sample was not collected properly, the test was taken too soon, or the test didn’t perform well.
  • False positive results
    • This means that the test result should be negative because you DO NOT have COVID-19 but instead it comes back positive.
    • This may happen, for example, if the person tested is very unlikely to be infected and the test didn’t perform well.

A downloadable infographic summary is available: Types of Coronavirus Tests

TESTING FOR CURRENT COVID-19 INFECTION: Diagnostic (Viral) Tests -
Molecular and Antigen Tests

Which Test is Recommended to Look for Current Infection
  • Molecular tests are recommended to check for current infection because they are better than antigen tests at detecting the virus that causes COVID-19.
  • Antigen tests are faster than most molecular tests, but they do not work as well.
    • If you have symptoms of COVID-19 and your antigen test result was negative, you need to have a molecular test to know if you have COVID-19 or not.
  • Serology tests are not recommended to look for current infection.
  • Ask your provider which type of test they are using.
When Testing is Recommended

Testing is highly recommended for:

  • People who have symptoms: If you have symptoms of COVID-19, talk to a healthcare provider and get tested.
  • People who have been a “close contact” to someone with confirmed or suspected COVID-19 (a case) within the last 14 days. Even if your test is negative, you will still need to complete your quarantine.
  • People with or without symptoms who are part of an outbreak response or contact investigation in high risk settings, such as nursing homes, congregate living facilities, correctional facilities, or persons experiencing homelessness.

In addition, people without symptoms who believe they may be currently infected should consider getting tested.

  • For instance, if in the past 2 weeks you were around many people who were not wearing face coverings and/or were not keeping a safe distance such as at your workplace or other indoor space.

Testing is not recommended for people who had a positive viral COVID-19 test in the last 90 days and do not currently have symptoms of COVID-19.

How To Get a Test
  • Call your healthcare provider. If you need help finding a health care provider, call 2-1-1 or visit the 211LA
  • People who live in LA County, regardless of immigration status, can apply for an appointment for a drive through or walk up test by visiting lacounty.gov/testing or by calling 2-1-1.
  • You can also get a test at some pharmacies. Check with your local pharmacy.
  • Beware of COVID-19 testing scams – visit our COVID-19 scams and fraud page for more information.
Paying For a Test to Diagnose COVID-19
  • Health insurers are required (by federal law) to cover the entire cost of testing for the virus whether you have symptoms or not. A doctor will need to order the test.
  • Testing through the County of Los Angeles and the City of Los Angeles mobile testing sites is free for all LA County residents who meet the criteria for testing, regardless of their immigration status.
Questions To Ask Before You Get A Test
  • What type of test you are being offered (see table).
  • How long it will take to get your results.
  • How you will find out the results.
  • What precautions you should take while you wait for your results and what you should do if your result is positive or is negative.

After the test, make sure that you understand what your result means and what to do next.

Understanding your viral test results and what to do next

Your COVID-19 Test was POSITIVE

A positive result means you have COVID-19. The test detected the COVID-19 virus.

You must isolate yourself:

  • If you’ve been sick, stay home away from others until:
    • At least 10 days have passed since you first felt sick and
    • You haven’t had a fever for 24 hours (without medication) and
    • Your symptoms have gotten better
  • If you never felt sick,  stay home away from others until 10 days after the test was taken.

Even if you had no symptoms, you are still infected and you can still pass the virus onto other people. If you start feeling sick, you must stay home longer, see If you’ve been sick above.


Tell all of your close contacts to quarantine: give them the quarantine instructions available at ph.lacounty.gov/covidquarantine.

Follow the full isolation instructions: ph.lacounty.gov/covidisolation.

Answer the call from LA Public Health: Help slow the spread of COVID-19 by answering if you get a call from “LA Public Health” or (833) 641-0305. You can also call (833) 540-0473.

Your COVID-19 Test was NEGATIVE

A negative COVID-19 result means the test did NOT detect the COVID-19 virus at the time you took the test. But it is possible that the test is wrong and that you are infected. This can happen if the test is taken too early or if the test misses your infection. Even if the result is correct, because there is so much COVID-19 around, you could become infected at any time. Practice everyday prevention including physical distancing, wearing a mask over your nose and mouth, and avoiding crowded places (especially indoors). 


  • If you have been sick AND your test was a PCR test, you should stay home until:
    • You have been fever-free without the help of fever-reducing medicines for at least 24 hours and
    • Your other symptoms have improved (unless your doctor told you to stay at home longer).
  • If you have been sick AND your test was a rapid antigen test, you should stay home and act like you have COVID-19 until you get the results of your PCR test.

This is because antigen tests often miss infections. See Information for Patients with Symptoms Who Have a Negative Antigen Test.

If you are not sure what kind test you got, look at your test result report, ask your provider, or look on the webpage where you booked the appointment.


  • If you have been feeling well BUT you have been exposed to someone with COVID-19 in the past 14 days (for example you are a close contact to a case or you were working or living where there were several people with COVID-19).

You may still be infected, but it is too early to show on the test.

You need to stay in quarantine for 10 days after you last had close contact with the person with COVID-19.

  • It is important to monitor your health for symptoms of COVID-19 for 14 days from your last contact with the infected person.

Follow the full quarantine instructions at ph.lacounty.gov/covidquarantine.


  • If you have been feeling well and you had no known exposures to anyone with COVID-19

You were probably not infected with COVID-19 on the day your test was taken.

  • Protect yourself and others from the daily risk of COVID-19.
  • Practice everyday prevention, including keeping your distance from others, wearing a mask correctly over both your nose and mouth, and washing your hands often. Choose wisely and avoid the 3 C’s (confined spaces, crowding, and close contact).

TESTING FOR PAST COVID-19 INFECTION: ANTIBODY TESTS (Serology)

Antibody tests (also known as serology tests) are blood tests that look for antibodies against a virus. They do not look for the virus itself. Antibodies are proteins that are made by the immune system to help fight infection. It takes about one to three weeks after the start of COVID-19 symptoms for the body to make enough antibodies to be found by a test. Some people may take even longer and some people who were infected with COVID-19 may never develop antibodies.

We do not know yet if having antibodies to the virus can protect someone from getting infected again, and if it does, how long that protection (immunity) might last. Until more is known, even if you had a positive antibody test, you should continue to practice everyday prevention to protect yourself and others, including keeping your physical distance from others, correctly wearing a mask, and washing your hands often. Continue to choose wisely and avoid the 3 C’s (confined spaces, crowding, and close contact).

Antibody test results should not be used to determine if someone can return to work or to decide who can spend time together.

To learn more about using antibody tests to look for past infection, visit the CDC webpage.

Uses of antibody tests

To guide the management of someone with complicated symptoms

There are situations where a serology test may be helpful (in addition to a viral test) to diagnose COVID-19, such as:

  • If someone develops complications late in an illness that may be associated with COVID-19, such as multisystem inflammatory syndrome in children (MIS-C).
  • If someone had symptoms of COVID-19 for several weeks and the viral tests were negative.

For science and public health

Scientists and Public Health organizations are using antibody tests to learn more about how the immune system responds to the COVID-19 virus over time. Antibody tests can tell how many people in a community may have been infected in the past and how far the pandemic has progressed. They can also be used to help understand why some people get infected but never show any symptoms (asymptomatic infection).

MORE INFORMATION

  • CDC COVID-19 Testing: webpage with links to pages on types of tests and FAQs
  • FDA Coronavirus Basics: Explains the different types of tests, and how they are performed and approved. PDF webpage
  • White House/DHHS Guidance on Interpreting COVID-19 test results: A one-page table on how to interpret test results (including when a combination of tests is done) and determining what actions to take according to the results.


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  • Public Health has made reasonable efforts to provide accurate translation. However, no computerized translation is perfect and is not intended to replace traditional translation methods. If questions arise concerning the accuracy of the information, please refer to the English edition of the website, which is the official version.

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